Ce-Containing Sintered NdFeB Magnets With Targeted Rare Earth Diffusion
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Solution Overview
Problem
The high cost of heavy rare earth elements in NdFeB sintered permanent magnets due to their high content in conventional manufacturing processes, which affects the magnetic coercivity and high-temperature resistance, necessitates a method to reduce the total content of these elements while maintaining or improving magnetic performance.
Innovation Solution
A method involving the use of cerium as a low-melting-point powder in combination with hydrogen embrittlement and jet milling, followed by magnetic field orientation molding, sintering, and diffusion heat treatment with a heavy rare earth alloy diffusion source to create a high-coercivity NdFeB magnet with reduced heavy rare earth content and enhanced high-temperature resistance.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Strength
If heavy rare earths (Tb or Dy) are directly mixed into the magnet alloy powders, then magnetic coercivity is greatly improved, but material cost increases significantly
Solution Approach 1:
The patent applies preliminary action by pre-coating the alloy flakes with a low melting point alloy layer containing heavy rare earths before mixing with the magnet alloy powders. This preliminary coating ensures that the heavy rare earths are strategically positioned at the grain boundaries during subsequent processing, achieving effective magnetic coercivity enhancement with reduced overall heavy rare earth content and lower material cost.
Solution Approach 2:
The patent implements local quality by concentrating the heavy rare earth elements specifically in the low melting point alloy coating layer at the grain boundaries, rather than uniformly distributing them throughout the entire magnet alloy. This localized concentration achieves the necessary magnetic coercivity improvement at the critical grain boundary regions while significantly reducing the total quantity of expensive heavy rare earth materials required.
2Quantity of substance
If the content of Ce in the magnet alloy is increased, then production cost is reduced, but magnetic performance deteriorates
Solution Approach 1:
The patent applies local quality by restricting heavy rare earth elements to the low melting point alloy coating layer at grain boundaries, while the bulk magnet alloy can utilize cheaper elements like Ce. This spatial differentiation allows the main body to use cost-effective materials while the critical grain boundary regions receive the necessary heavy rare earth concentration to maintain magnetic performance, thus reducing overall production cost without sacrificing magnetic properties.
Solution Approach 2:
The patent employs composite materials by creating a multi-layered structure where a low melting point alloy coating containing heavy rare earths is applied over alloy flakes that form the magnet alloy matrix. This composite structure combines the advantages of both materials: the bulk alloy provides the primary magnetic properties with cost-effective composition (including Ce), while the coating layer provides the necessary grain boundary modification with heavy rare earths to maintain performance.
3Quantity of substance
If Ce-containing diffusion source is used, then production cost is reduced, but high-temperature resistance deteriorates
Solution Approach 1:
The patent applies parameter changes by carefully controlling the composition of the low melting point alloy coating, specifically adjusting the ratios of heavy rare earths (Tb and/or Dy) combined with elements like Al, Cu, Ga, Ti, Co, Mg, Zn, or Sn. By optimizing these compositional parameters, the coating provides sufficient grain boundary modification to maintain high-temperature resistance while utilizing cost-effective elements, thereby reducing production cost without sacrificing thermal stability.
Solution Approach 2:
The patent uses composite materials in the low melting point alloy coating by combining heavy rare earth elements (for magnetic performance and high-temperature resistance) with other elements (Al, Cu, Ga, Ti, Co, Mg, Zn, or Sn) that can enhance structural stability at elevated temperatures. This composite coating structure achieves both cost reduction and maintenance of high-temperature resistance by leveraging the synergistic effects of different elements.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
The method significantly increases coercivity and high-temperature resistance of the NdFeB magnet, achieving comparable performance to pure Tb metal diffusion while reducing production costs and enabling mass production of low-cost high-coercivity sintered NdFeB magnets.
Implementation Method 1
subjecting the mixture to a hydrogen embrittlement process followed in this order by pulverizing the process product to an alloy powder by jet milling
Implementation Method 2
sintering and aging treatment the blank
Implementation Method 3
Performing a diffusion heat treatment so as to diffuse the diffusion source into the sintered NdFeB magnet
Implementation Method 4
the low melting point powder is at least one of CeαAl100-α with 90≤α≤99, CeβCu1-β with 80≤β≤99 and CeγGa1-βwith 80≤γ≤99
Data Source
AI summary
The disclosure relates to the technical field of sintered type NdFeB permanent magnets, in particular to a low-cost rare earth magnet and manufacturing method. There is provided a method of preparing a high-coercivity sintered NdFeB magnet including cerium comprising the following steps: (S1) providing alloy flakes composed of RxT(1-x-y-z)ByMz; (S2) mixing the alloy flakes, a low melting point powder, and a lubricant, then subjecting the mixture to a hydrogen embrittlement process followed in this order by pulverizing the process product to an alloy powder by jet milling, magnetic field orientation molding of the allow powder to obtain a blank, sintering and aging treatment the blank; (S3) coating a film composed of a diffusion source of formula R1xR2yHzM1-x-y-z on the sintered NdFeB magnet; and (S4) performing a diffusion heat treatment, followed by aging the sintered NdFeB magnet to obtain the low-cost rare earth magnet.